Olfactory system; sense of smell
Olfaction is sense of smell. In human sense of smell is received by nose.
Olfactory receptor neurons sends impulse via olfactory nerve (first cranial nerve).
Olfactory nerve; first cranial nerves
Olfactory nerve is sensory nerves pathway of smell. They originate as specialized olfactory nerve endings (chemoreceptors) in mucus membrane of roof of nasal cavity above superior nasal conchae.
On each side of nasal septum nerve fibers pass through cribriform plate of ethmoid bone of olfactory bulb where interconnections and synapse occur.
From bulb, bundles of nerve fibres from olfactory tract, which passes backwards to olfactory area in temporal lobe of cerebral cortex in each hemisphere.
Where impulse are interpreted and odour perceived.
Anatomy of olfactory epithelium
1. Olfactory epithelium consist cells;
Olfactory receptors; olfactory sensory neurons/receptor response to chemical stimulation.
Supporting cells; help detoxify chemical that come in contact with olfactory epithelium.
Basal cell; regeneration of olfactory receptors cells every 30-60 days.
2. Olfactory gland
Produce mucus that moisten surface of olfactory epithelium and dissolve odorants.
Also innervates by facial nerve branches and impulse of these branches can stimulate lacrimal glands in eye and nasal mucus gland.
Pathophysiology of smell; olfaction
Olfactory receptors react to odorant molecules, carried into nose with inhaled air, when dissolve in mucus, stimulate olfactory chemoreceptor odorant binds to olfactory receptor.
Olfactiory receptor Activated
Generation of nerve impulse (action potential)
Propagation along olfactory nerve
Synapse with olfactory bulb neuron olfactory tract;
1. Primary olfactory tract
Consciousness awareness of smell.
Temporal lobe, smell interpreted identified.
2. Hypothalamus and limbic system
Emotional and memory evoked response of ordor.
For example; hospital smell, favorite food and least liked food.
Olfactory sensation are only sensation that reach cerebral cortex without synapsing in thalamus.
Inflammation of nasal mucosa prevent odors substance from reaching olfactory area of nose, causing loss of sense of smell (anosmia).
Adaptation; when individual continuously exposed to odour perception of odor decrease and ceases with in few minutes.
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